• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.5
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• pp.367-375
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• 2022

Generally, a proportional-resonant controller is used to eliminate steady-state errors during the voltage-current control of a double-conversion uninterruptible power supply (UPS) in a stationary reference frame. Additionally, the feed-forward control compensating for the load current, which can be considered a disturbance of the voltage controller, can be used to improve the disturbance rejection performance. However, during the parallel operation of UPSs, circulating current can occur between UPS modules when performing both feed-forward control and droop control because feed-forward control reduces the circulating current impedance. This study proposes a feed-forward compensation technique that considers the impedance of circulating current. An additional feed-forward compensation technique is developed to enhance the disturbance rejection performance. The validity of the proposed feed-forward compensation technique is verified by the experiment results of the parallel operation of a 500 W double-conversion UPS module.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.5
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• pp.1011-1016
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• 2011

This paper presents a robust current controller for a surface-mounted permanent magnet synchronous motor(SPMSM) by using a PI observer. The decoupling PI(proportional-integral) controller combined with an additional feed-forward compensation has been used for the current controller. The classical feed-forward compensation using velocity information and system parameters is not expected to achieve a robust performance against parameter uncertainties. This paper has adopted a PI observer for the feed-forward compensation to cope with parameter uncertainties without using velocity information. A simple PI observer has been designed to compensate the disturbances that represent velocity coupled terms and parameter uncertainties. Experimental results as well as computer simulations with 630W SPMSM confirm that the proposed approach can deal with the effects of the disturbance and improve the control performance.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.6
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• pp.373-380
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• 2018

This study proposes a new islanding detection method that uses the phase shift of feed-forward voltage and evaluates the performance of an existing method and the proposed method when the grid frequency changes within the allowable range under steady-state conditions. The investigated existing method, which is slip mode frequency shift (SMS), uses current phase shift to detect islanding. The SMS method supplies reactive current to the grid under this condition, but the proposed method does not generate additional reactive power because it does not depend on the current control loop. The performance in steady-state grid condition is evaluated through simulations and experiments.

• Journal of IKEEE
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• v.21 no.4
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• pp.331-337
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• 2017

In this paper, we present the design of a 20MHz bandwidth 3rd-order continuous-time low-pass sigma-delta modulator with low-noise and low-power consumption. The bandwidth of the system is sufficient to accommodate LTE and other wireless network standards. The 3rd-order low-pass filter with feed-forward architecture achieves the low-power consumption as well as the low complexity. The system uses 3bit flash quantizer to provide fast data conversion. The current-steering DAC achieves low-power and improved sensitivity without additional circuitries. Cross-coupled transistors are adopted to reduce the current glitches. The proposed system achieves a peak SNDR of 65.9dB with 20MHz bandwidth and power consumption of 32.65mW. The in-band IM3 is simulated to be 69dBc with 600mVp-p two tone input tones. The circuit is designed in a 0.18-um CMOS technology and is driven by 500MHz sampling rate signal.

• Tunnel and Underground Space
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• v.30 no.1
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• pp.63-75
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• 2020

When tunnel is excavated via drilling and blasting, the excessive overbreak is the primary cause of personal or equipment safety hazards and increasing the cost of the tunnel operation owing to additional ground supports such as shotcrete. The practical management of overbreak is extremely difficult due to the complex causative mechanism of it. The study examines the relationship between rock mass characteristics (unsupported face condition, uniaxial compressive strength, face weathering and alteration, discontinuities- frequency, condition and angle between discontinuities and tunnel contour) and the depth of overbreak through using feed-forward artificial neuron networks. Then, Overbreak Resistance Factor (ORF) has been developed based on the weights of rock mass parameters to the overbreak phenomenon. Also, a new concept of tunnel overbreak management system using ORF has been suggested.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.3
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• pp.1434-1449
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• 2019

Video object segmentation is a significant task in computer vision, but its performance is not very satisfactory. A method of video object segmentation using weakly temporal information is presented in this paper. Motivated by the phenomenon in reality that the motion of the object is a continuous and smooth process and the appearance of the object does not change much between adjacent frames in the video sequences, we use a feed-forward architecture with motion estimation to predict the mask of the current frame. We extend an additional mask channel for the previous frame segmentation result. The mask of the previous frame is treated as the input of the expanded channel after processing, and then we extract the temporal feature of the object and fuse it with other feature maps to generate the final mask. In addition, we introduce multi-mask guidance to improve the stability of the model. Moreover, we enhance segmentation performance by further training with the masks already obtained. Experiments show that our method achieves competitive results on DAVIS-2016 on single object segmentation compared to some state-of-the-art algorithms.

• The Journal of the Acoustical Society of Korea
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• v.40 no.2
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• pp.121-129
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• 2021

This paper deals with a super-resolution that improves the resolution of side scan sonar images using learning-based compressive sensing. Learning-based compressive sensing combined with deep learning and compressive sensing takes a structure of a feed-forward network and parameters are set automatically through learning. In particular, we propose a method that can effectively extract additional information required in the super-resolution process through various initialization methods. Representative experimental results show that the proposed method provides improved performance in terms of Peak Signal-to-Noise Ratio (PSNR) and Structure Similarity Index Measure (SSIM) than conventional methods.

• Membrane Journal
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• v.26 no.3
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• pp.187-196
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• 2016

Pressure-assisted forward osmosis (PAFO) process has recently been under spotlight for its potential to improve forward osmosis (FO) process performance by applying low hydraulic pressure on the feed side. Structure parameter, one of the governing factors in estimating water flux and solute flux across FO membranes in the solution-diffusion model (S-D model), determines solute resistivity in FO and PAFO processes. This study aims to estimate the trend of structure parameter change with respect to varying additional hydraulic pressure condition in PAFO.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.4
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• pp.283-290
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• 2022

This study proposes a voltage control scheme in a synchronous reference frame to improve the dynamic characteristics of double-conversion UPSs. UPSs need to control positive and negative sequence voltage, so that positive and negative sequence extractors are generally used to obtain each sequence of the voltage and current. Voltage and current controllers for each sequence are implemented. However, the extractor causes considerable delay, and the delay restricts the control performance, especially for the current controller. To improve the dynamics of the current controller, the proposed scheme adopts a unified current controller without separating positive and negative sequences. By using discrete-time current controller, the control bandwidth can be extended significantly so that negative sequence current can be controlled. To enhance the performance, an additional feed-forward technique for output voltage regulation is proposed. The validity of the proposed controller is verified by experiments.

• PNF and Movement
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• v.5 no.1
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• pp.19-28
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• 2007

Proprioception means the ability to perceive the sensation of position and movement of body. As it is transmitted to central nervous system and used in feed-back or feed-forward motor control, proprioception allows us to keep our normal movement and normal balance activity. However, the conditions such as injury, disease, aging and fatigue can damage the proprioceptiive sensation of position, movement and lead to a functional impairment and additional damages in musculoskeletal system, because they alter the amount of proprioceptive ability that transfer into the central nervous system. The purpose of this study was to identify the definition and the function of proprioception, to look into variations in injury, disease, aging and fatigue that can be easily met in clinical application and eventually to provide valuable aid for assessment and treatment.